This invention relates to a plated product in which the surface of a metallic or nonmetallic material is plated, and to a method and apparatus for producing it.
2 Prior Art
When the surface of a metallic or nonmetallic material is to be plated, it has been conventionally attempted to form fine recesses on the material before plating it, so as to enhance the adhesion of the material with a thin film of metal (plating). To form the recesses, various methods have been proposed. For example, in a certain method, fine powder particles are caused to hit the material. In another method, a certain kind of substance or fine particles that are dissolvable in a specified solution are previously embedded near the surface of the material, or mixed with the material, and the substance or fine particles are then dissolved in the solution.
In the former method, the sizes of the fine powder particles range from several tens to several hundreds of .mu.m. Therefore, the fine recesses are formed by plastic deformation or a cutting force resulting from the collisions of the powder particles with the material to be plated. FIG. 1(a) shows a recess mainly formed by the plastic deformation made by the powder particles hitting the surface of the material at substantially right angles to it. FIG. 1(b) shows a recess mainly formed by the cutting force formed by the powder particles hitting the surface of the material at an acute angle of incidence to the surface. Each of these recesses has a form that opens outwards, like a state after a meteorite has collided with a planet. Therefore, when the surface of the material is plated, the adhesion of the thin film of metal to the surface depends on the thin film of metal's own adhesive force, the resistance due to the uneven surface of the material, and the area of adhesion. Therefore, the following problems have occurred:
When a force is applied in a direction substantially parallel to the surface of the material, not only the thin film of metal's own adhesive force, but also a resistant force (peeling resistance) is generated, in response to the resistance due to the uneven surface of the material, and to the size of the area where the metal adheres to the surface of the material to be plated. When a force is applied at substantially right angles to the surface of the material, the adhesion of the thin film of metal to the surface of the material depends only on the adhesion force of the thin film of metal, and the resistance due to the uneven surface of the material and the size of the adhered area do not contribute to the retention of the thin film of metal on the surface of the material. Thus, when a mechanically great force such as a strong hitting force is applied to a part of the plated surface, a phenomenon of fine peeling occurs on that part of the plating. Further, if the force is repeated, then the peeling increases, so that the thin film of metal peels off the material.
In the latter method, the sizes of the fine recesses on the surface of the material depend on the sizes of the substance or the particles embedded or mixed. The sizes of the fine recesses are less than 2.about.3 .mu.m. As in FIG. 2 (a), the size of the opening of a recess is small as compared with the size of the entire recess. Therefore, in plating a material, the metal tends not to enter the recess. FIG. 2(b) shows that the thin film of metal only blocks the opening of the recess. This leads to the adhesion of the thin film of metal to the surface of the material depending only on the thin film of metal's own adhesive force. Thus, when a mechanically large force is applied to the plated material, and is applied to a particular point on its surface, at right angles, the thin film of metal at that point peels off the material.